Recently, there is business to deliver, for example, a commodity to home of a commodity purchaser. In this delivery business, for example, in a case where the purchaser is away from the place where the commodity is delivered, a deliverer leaves an absence notification at the home of the commodity purchaser. Specifically, the deliverer issues a label or a receipt on which information of the absence notification is printed by using a portable printer and leaves the issued absence notification at the home of the commodity purchaser. Here, the information of the absence notification corresponds to, for example, information in which the purchased commodity is unable to be delivered and temporarily stored because the commodity purchaser is not at home or the like. Such a portable printer has a battery for its operation. An operator of the printer (deliverer) recognizes a battery remaining amount based on a battery residual capacity shown by the printer.
As described above, although the printer informs the operator that the battery residual capacity of the installed battery becomes low, it is difficult for the operator to recognize how many the labels or the receipts can be furthermore printed by the printer.